The invention relates to apparatus for providing an electrical connection path into equipment in an underwater, wet or conductive environment.
Underwater penetrators are used to provide an electrical connection path through a sealed interface into underwater equipment, for example to connect electrically a conductor of an underwater cable to equipment such as a pump. The conductor of the cable is terminated in a gland assembly which provides a sealed enclosure protecting a connection of the cable conductor to what is commonly referred to as a “penetrator pin”. The penetrator pin typically consists of a copper conductive core surrounded by a sleeve of insulating material. The penetrator pin is supported by and passes axially through a metal support flange of the penetrator.
The insulation of the cable may be sealed to the gland assembly by various means including elastomeric seals and encapsulation. The sealed region of the gland assembly may be filled with oil or the like and have one or more flexible diaphragms or walls to allow the pressure inside the assembly to balance with respect to the external pressure and so avoid any tendency for water or other contamination to enter into the gland assembly. The penetrator pin is therefore pressure compensated external of the equipment such as a pump by the gland assembly, but there may be pressure differentials from one end of the penetrator pin to the other (gland end to equipment end), resulting in positive or negative pressure differentials acting directly on the penetrator pin.
A known penetrator pin is shown in FIG. 1. The penetrator pin 1 has a copper conductive core 2 surrounded by an insulating sleeve 3 made of epoxy resin. The penetrator pin extends across an interface between a gland assembly 4 and an item of underwater equipment (not shown). At its gland assembly end, the conductive core 2 is connected to a conductor 17 of an underwater cable. A diaphragm support ring 18 supports one end of diaphragms 19 which protect the conductor 17 and its connection to the conductive core 2 of the penetrator pin. At its other end, the conductive core 2 is connected to the underwater equipment (the connection is not shown). The penetrator pin is supported by a support flange 5. The flange is secured by bolts 6 to the gland assembly 4 and by bolts 7 to a mating flange 8 which forms part of the underwater equipment. The support flange 5 is formed with an axial socket 9 which receives the penetrator pin 1.
The penetrator pin 1 has an annular flange 10 which projects radially outwardly from the central part of the penetrator pin. The flange 10 is supported in the support flange socket 9 between a first compliant seal 11 engaging one annular axial face of the flange 10 and a second compliant seal 12 engaging the opposite annular axial face of the flange 10. A retaining ring 13 is screwed into position to clamp the flange 10 against a shoulder 14 of the socket 9, with the sealing rings 11 and 12 providing resilient bearing surfaces for the flange 10. Due to differential pressures at the gland end and equipment end of the penetrator pin 1, it is subject to axial thrust forces which have to be resisted by the flange 10 carried by the penetrator support flange 5.
A generally cylindrical earth screen 15, made of copper mesh, is embedded in the epoxy resin insulating sleeve 3 and is electrically connected to the penetrator support flange 5 by radially extending conductors 16. The purpose of the earth screen 15 is to protect the insulating sleeve 3 from high electrical stresses in regions of the sleeve where there would otherwise be electrical stress concentration, such as where the epoxy resin is in close proximity to the shoulder 14 of the penetrator support flange 5. Lines of equal electric potential in the epoxy resin become closely spaced at such a discontinuity in the shape of the earthed support flange 5. The electrical stresses can be significant where high voltages are involved, for example at 14 kV and above.
The earth screen 15 is positioned between the conductive core 2 and the support flange 5 and so screens the epoxy material radially outwardly of the earth screen 15, whereby high electrical stresses are reduced and diverted away from such problem areas. The screen itself is generally cylindrical with curved, flared axial ends, so avoiding sharp discontinuities and hence the creation of high electrical stress concentrations in the epoxy resin material radially inwardly of the screen.
Whilst the arrangement of FIG. 1 has been used successfully in the past, the present inventors have now recognised that the provision of the earth screen embedded in the material of the insulating sleeve creates a discontinuity in what would otherwise be a homogeneous material and a potential mechanical weakness, in particular a cylindrical surface along which the insulating sleeve material may shear under the axial loading on the penetrator pin caused by pressure differentials between the gland assembly end and the equipment end.